Polymer of 4-carboxy-2-piperidone

ABSTRACT

4-CARBOXY-2-PIPERIDONE POLYMERIZES READILY ON HEATING ABOVE ITS MELTING POINT TO AFFORD A POLYMER CONSISTING ESSENTIALLY OF RECURRING UNITS OF THE STRUCTURE:   -((CH2)2-(2,5-DI(O=)PYRROLIDIN-3,1-YLENE))-   THIS POLYMER FORMS TRANSPARENT FILMS, FILAMENTS, AND COATINGS OF HIGH STRENGTH AND GLASS TRANSTITION TEMPERATURE.

United States Patent 3,634,363 POLYMER 01F 4-CARBOXY-2-PIPERIDONE GeorgeJ. Schmitt, Madison, and Karl P. Klein and Herbert K. Reimschnessel,Morristown, N.J., assignors to Allied Chemical Corporation, New York,N.Y. N0 Drawing. Filed Feb. 26, 11969, Ser. No. 802,673 Int. Cl. (108g20/10 US. Cl. 260-78 P 5 Claims ABSTRACT OF THE DISCLOSURE4-carboxy-2-piperidone polymerizes readily on heating above its meltingpoint to afford a polymer consisting essentially of recurring units ofthe structure:

This polymer forms transparent films, filaments, and coatings of highstrength and glass transition temperature.

CROSS-REFERENCES TO RELATED APPLICATIONS 4-carboxy-2-piperidone and aprocess for the preparation thereof are claimed in our copending,commonly assigned, application Ser. No. 802,630, entitled Process forthe Preparation of 4-Carboxy-2-Piperidone and Esters Thereof, filed oninstant date herewith.

BACKGROUND OF THE INVENTION Thermoplastics such as nylon 6 have achievedvery widespread usage. However, it is indisputable that no thermoplasticcurrently available has ideal properties for all uses. One or moreshortcomings are always present. There is, therefore, always a need fora new thermoplastic that can be readily prepared from cheap and easilyobtainable monomers.

It is an object of this invention to provide a novel high molecularweight thermoplastic polymer that can be readily formed by conventionalthermoplastic polymerforming procedures into transparent films,filaments and coatings of high strength and glass transitiontemperature.

It is a further object of this invention to provide a novelthermoplastic polymer that is easily prepared from inexpensive, simpleto-make starting materials.

Further objects and advantages will become apparent from the descriptionof the invention which follows in greater detail.

The polymers of the instant invention are prepared from4-carboxy-2-piperidone:

( COOH the structure:

that is, a poly(2,5-dioxo-1,3-pyrrolidinediyl) dimethylene.

'ice

The preparation of polymers from lactams is known. The seven-memberedring, i.e., E-caprolactam, is, of course, the starting material fornylon 6; however, polymerization of the corresponding fiveandsix-membered lactam rings, i.e., a-pyrrolidone and a-piperidone, is notwidely practiced.

Polymerization of ot-pyrrolidone in the presence of basic catalysts toform the linear polymer, poly-4-butyramide, is reported in US. Pats.Nos. 2,638,463; 2,734,043 and 2,739,959.

Polymerization of u-piperidone was at first believed to be impossible-J.Am. Chem. Soc., 52, 5289 (1930), ibid 80, 6406 (1958); Trans. FaradaySoc., 51, 1717 (1955). More recently, the catalytic polymerization ofwpiperidone has been reportedU.S. Pat. No. 2,806,841, J. Pol. Sci., 43,117 (1960).

It has been shown that the application of heat alone does not effectpolymerization of previously known lacterms. The conversion of suchlactams to linear polyamides is accomplished by catalytic processes thatmay be either hydrolytic or nonhydrolytic. Generally, lactams with sixor more carbon atoms may be polymerized by either type process, whereasonly a nonhydrolytic process is suitable for the polymerization oflactams with less than six carbon atoms. In the latter cases, water wasfound to have a very serious inhibitory effect on the polymerization.

An article [Markrornol Chemic, 80, 44 (1964)] reports thatmono-substituted-a-piperidones are unpolymerizable by any method.

It has now been found in accordance with the instant invention that thepolymerization of compound (I) can be effected by heat alone and in theabsence of any additional catalyst.

The process is carried out in the absence of oxygen. The exclusion ofoxygen can be achieved by evacuation of the polymerization vessel or bymaintaining an atmosphere of an inert gas such as nitrogen, helium,argon, or carbon dioxide in said vessel. The latter method of exeludingoxygen is generally preferable from a convenience standpoint.

Although the polymerization of 4-carboxy-2-piperidone can be achieved byheat alone, no deleterious effects are observed when the polymerizationis conducted in the presence of small amount of water.

In effecting polymerization, compound (I) can be heated either neat ordispersed in a refluxing, high-boiling, inert liquid rnenstruum. Theterm dispersed as used herein connotes that compound (I) can be eitherfully dissolved in said liquid rnenstruum and suspended therein infinely particulate form or partially dissolved and partially suspendedtherein. Suitable liquids include o-dichlorobenzene, trichlorobenzene,Tetralin, Decalin, mineral oil, and silicone oil.

Since the polymerization results in the production of 1 mol of water permol of compound (I), polymerization is preferably effected in arefluxing solvent such as dior trichlorobenzene, Tetralin or Decalin ina polymerization vessel equipped with an apparatus such as Dean Starketrap which enables the water produced in the polymerization to beentrained off by the refluxing solvent.

The heating temperature necessary to effect polymerization can vary fromat least C. up to about 250 C. Temperatures above 250 C., although notin any way inoperable, serve no useful purpose and may cause a smallamount of thermal degradation of the polymer. The preferredpolymerization temperature is about 180 to 220 C.

The duration of heating to effect polymerization will vary with thetemperature and degree of polymerization (DP) desired. In general, thehigher the temperature, the more rapid the polymerization, and thelonger the heat- 2.? ing, the greater the DI achieved. Noticeablethickening is achieved by heating compound (I) at 150 C. for 1 hour.High molecular weight polymer is obtained by heating for up to about 24hours. Still longer heating does not cause any significant furtherincrease in molecular weight although it is not harmful. The polymer,after formation, can be poured out of the polymerization vessel inmolten form, if polymerization has been effected without a dispersingliquid. If a dispersing liquid is used, the polymer can be separatedtherefrom by decantation or filtration, for example.

The polymer is soluble in formic acid, meta-cresol, trifiuoroethanol,and sulfuric acid. It is an amorphous thermoplastic that can be readilyformed into virtually any desired shape, including films and filaments,by conventional processing methods such as extrusion; blow, compressionor injection molding; or melt or solution casting.

The 4-carboxy-2-piperidone monomeric starting material and the processfor the preparation thereof is dis closed and claimed in our copending,commonly assigned, application Ser. No. 802,630, entitled Process forthe Preparation of 4 Carboxy 2 Piperidone and Esters Thereof, filed oninstant date herewith, the pertinent portions of which are herebyincorporated by reference. In essence, we have found that4-alkoxycarbonyl-Z-piperidones can be prepared in only two steps, bothof which afford high yields, from dialkyl esters of itaconic acid.

The two-step reaction can be represented as follows:

wherein R in compounds (III), (IV) and (V) represents an alkyl group of1-10 carbon atoms. The free acid, 4-carboxy-2-piperidone:

can be prepared from the ester (V) by conventional ester saponificationwith base followed by acidification. This compound is unknown to theprior art.

The instant invention can be more fully understood by reference to thefollowing examples. All parts are parts by weight unless otherwiseexpressly noted.

EXAMPLE 1 Five parts of 4-carboxy-2-piperidone and 0.2 part of waterwere placed in a Pyrex polymerization tube fitted with a gas inlet tube.The Pyrex tube was swept with nitrogen and then immersed in an oil bathmaintained at a constant temperature of 220 C. After 24 hours, thepolymerization tube was removed from the bath and allowed to cool toroom temperature while maintaining a continuous nitrogen sweep. Aftercooling, the tube was broken away from the polymer plug, which wasground. After extraction in boiling ethanol With subsequent drying at100 C. and 30 mm. Hg, the ground polymer sample exhibited a reducedviscosity of 0.8, when measured using an 0.13- gram sample in 25 cc. ofmeta-cresol solution at 25 C.

The spectral data of the polymer samples were consistent with thepolyimide structure: Infrared analysis film showed a strong absorptionpeak at 1700l740 cm. (imide C=O); nuclear magnetic resonance (NMR)analysis (15% polymer in formic acid) showed peaks at 1.17- 2.13(complex multiplet, NCH CH CH); 2.44 (multiplet, COCH and 3.26(multiplet, NCH

EXAMPLE 2 Two samples of 4-carboxy-2-piperidone were heated to 200 C.and 220 C., respectively, in a nitrogen sweep for 20 hours and thenmaintained at this temperature an additional 20 hours under vacuum (2mm. Hg). The polyier samples, when worked up as in Example 1, hadreduced viscosity values of 1.0 and 1.4, respectively, when measuredusing an 0.13-grarn sample in 25 cc. of metacresol at 25 C. The infraredspectra of these samples were identical to that of polymer from Example1.

EXAMPLE 3 One hundred grams of particulate 4-carboxy-2-pipcridone wasdispersed in 2000 cc. of refluxing dichlorobenzene for 48 hours.Nitrogen was bubbled through the dispersion during this period. Thewater formed during the polymerization was removed by passing thedichlorobenzene reflux vapors through a Soxhlet apparatus containinganhydrous magnesium sulfate. After cooling the reaction mixture to roomtemperature, dichlorobenzene was decanted and the polymeric precipitatedissolved in formic acid. The resulting solution was filtered and thefiltrate added dropwise to ether. The polymer which precipitated waswashed with ethanol at room temperature and then extracted with boilingethanol. After drying at C. and 30 mm. Hg, the reduced viscosity of thepolymer was 0.5, when measured using an 0.13-gram sample in 25 cc. ofmeta-cresol at 25 C.

The polymer was pressure molded at 235 C. into films which were testedon an Instron testing apparatus, the tensile values are listed in TableI.

TABLE I.TENSILE VALUES Fifty grams of 4-carboxy-2-piperidone waspolymerized in refluxing trichlorobenzene and worked up, as describedfor the polymerization of Example 3. The resulting polymer had a reducedviscosity of 1.5 when measured using an 0.13-gram sample in 25 cc., ofmeta-cresol at 25 C. Differential thermal analysis measurementsindicated that the polymer had a glass transition temperature of 127 C.When heated at a rate of 20 C./minute. When heated to 250 C., quenchedand re-heated at 20 C./minute, the glass transition temperature of thepolymer sample was C. Thermal gravimetric analysis measurements showedthat the polymer experienced a 1% weight loss in either air or N at 300C. when heated at a rate of 10 C./ minute. Table II gives results of thetesting of films pressure molded from the polymer at 250280 C TABLEII.TENSILE VALUES Dimethyl cyanomethyl succinate To a stirred solutionof 79.0 grams (0.5 mol) of distilled dnnethyl itaconate in 400 ml. ofmethanol cooled to 2 C. was added dropwise 65.1 grams (1 mol) ofpotassium cyanide in 400 ml. of Water. After /2 hour, 65 ml. (0.75 mol)of cold concentrated hydrochloric acid was added. The reaction mixturewas stirred at room temperature for 72 hours and then extracted withthree portions of ether. The ethereal extracts were combined, dried overMgSO filtered, and solvent evaporated. The resulting oil was distilledat reduced pressure to afford 71.4 grams (77%) of dimethyl cyanomethylsuccinate, boiling point 1l32-117 C. at 0.8 mm. Hg.

Infrared analysis (neat) showed strong absorption bands at 2260 cm.(GEN) 1745 cm.- (CEO).

Elemental analysis-Calculated for C H NO .-Theory (percent): C, 51.88;H, 5.99; N, 7.57. Found (percent): C, 51.58; H, 5.76; N, 7.76.

EXAMPLE 6 4-methoxycarbonyl-Z-piperidone A solution of dimethylcyanomethyl succinate (46.3 g.) (0.25 mol) in 250 cc. methanol washydrogenated at 400 p.s.i. and 100 C. for hours using a Raney nickelcatalyst (4 grams). Following hydrogenation, the solution was filteredto remove the catalyst and the methanol evaporated at reduced pressure.The resulting solid residue was recrystallized from petroleumether/methylene chloride to give 33.8 g. (86%) of4-methoxycarbonyl-2-piperidone, melting point 126.5 -l27 C. Infraredanalysis (KBr pellet) showed strong absorption bands at 1740 cm. (esterC=O), 1665 cm.- (lactam C O).

Elemental andlysis.-Calculated for C H NO .-Theory (percent): C, 53.49;H, 7.06; N, 8.91. Found (percent): C, 53.33; H, 7.14; N, 8.92.

EXAMPLE 7 4-carboxy-2-piperidone To a stirred solution of 12.3 g. (0.22mol) of potassium hydroxide in 150 ml. of methanol was added 31.4 g.(0.2 mol) of 4-methoxycarbonyl-2-piperidone in 150 ml. of methanol. Thesolution was refluxed for 6 hr. and allowed to stir at room temperaturefor 16 hr. The solvent was then removed at reduced pressure. Theresulting solid was dissolved in 50 ml. of water, cooled to about 0 C,and acidified with concentrated hydrochloric acid. Threerecrystallizations of the precipitate from ethanol/water yielded 25.5 g.(89%) of 4-carboxy-2-piperidone, melting point 174.5 -175.5 C. Infraredanalysis (KBr pellet) showed strong absorption bands at 1695 cm." (acidC 0) and 1635 cm. (lactam C'=O).

Elemental analysis-Calculated for C H NO .-Theory (percent): C, 50.34; H6.34; N, 9.79. Found (percent):C, 50.36; H, 6.36; N, 9.60.

Various modifications will be apparent to one skiled in the art, and itis not intended that this invention be limited to the details in thespecific examples presented by Way of illustration. Accordingly, thescope of the invention is limited only by the appended claims.

We claim:

1. A thermoplastic polymer consisting essentially of recurring units ofthe structure:

0 CHz-Hl l 2. A process for producing the polymer of claim 1 consistingof heating 4-carboxy-2-piperid0ne under oxygenfree conditions at atemperature of at least about C. for a time sufiicient to effectpolymerization thereof.

3. A process in accordance with claim 2 wherein said temperature rangesfrom about to about 220 C.

4. A process in accordance with claim 2 wherein said4-carboxy-2-piperidone is dispersed in a high-boiling, inert liquidmenstruum.

5. A process in accordance with claim 4 wherein said liquid is selectedfrom the group consisting of o-dichlorobenzene, trichlorobenzene,Tetralin and Decalin and wherein said liquid is heated to reflux.

References Cited UNITED STATES PATENTS 2,421,024 5/ 1947 Frosch 260-782,502,576 4/1950 Lincoln et al 260-78 2,865,895 12/1958 Pieper et a1260-78 3,022,274 2/ 1962 Glickman et al. 260-78 3,061,592 10/1962Schnell et a1. 260-78 3,158,589 11/1964 Glickman et 'al 260-78 3,174,9513/1965 Taber 260-78 3,384,625 5/ 1968 Reimschuessel 260-78 3,405,09910/1968 Taber 260-78 3,422,093 l/1969 Reimschuessel et al. 260-783,448,086 6/ 1969 Bachman et al. 260-78 3,542,744 11/1970 Reimscheusselet a1. 260-78 L HAROLD D. ANDERSON, Primary Examiner U.S. Cl. X.R.

260-30.8 R, 31.2 N, 33.4 R

